As the dimensions of transistor devices continue to shrink, various issues arise imposing increasing demands for methodology enabling the fabrication of semiconductor devices having high reliability and high circuit speed. Smaller transistors allow more transistors to be placed on a single substrate, thereby allowing relatively large circuit systems to be incorporated on a single, relatively small die area. However, smaller transistors require reduced feature sizes. As the gate width for transistors decreases, the gate dielectric thickness decreases as well. The decrease in gate oxide thickness is driven in part by the demands of overall device scaling. As gate conductor widths decrease, for example, other device dimensions must also decrease in order to maintain proper device operation. For 22 nanometer (nm) technology nodes and beyond, it is becoming critical to deposit films less than 50 Å.
Thin films formed from, for example, silicon (Si), silicon carbide (SiC), silicon-germanium (Si1-xGex), silicon nitride (Si1-xNx), silicon oxide (SiOx), and the like, find widespread use in the fabrication of semiconductor devices. One approach for forming such thin films on a substrate is through chemical vapor deposition (CVD). Currently depositing films thinner than 50 Å by CVD is difficult because the resulting films are generally discontinuous. The discontinuity is due in part to nucleation and growth phenomena, but more importantly is due to non-uniformities inherent to a CVD tool. Each showerhead in a CVD tool imparts some non-uniformity in the deposited film due to imperfections or subtle, unique flow characteristics.
Novellus has addressed the uniformity problem by using multiple showerhead, or chuck, deposition. In a Novellus tool, the wafer is moved to four or five different chucks for deposition of a portion of the film at each chuck. Since each showerhead introduces its own random non-uniformities, using several chucks is believed to average out the non-uniformities of each. However, it is possible for the non-uniformities of one showerhead to align with those of another. Furthermore, the Novellus solution requires four or more chucks, resulting in a complex and costly system.
A need therefore exists for efficient and cost effective methodology and tools enabling the deposition of ultra thin films with superior within wafer uniformity and excellent repeatability from wafer to wafer.